On the identification of molybdophosphate complexes in aqueous solution

Abstract

Aqueous solutions containing sodium phosphate and sodium molybdate ([P]= 0.01–0.07 mol l–1[Mo] : [P]= 1.25–15) were acidified with concentrated HCl and the formation of molybdophosphate anions was followed by 31P n.m.r. spectroscopy with a view to establishing this technique as an easily applicable method for the identification of molybdophosphate species in solution. For comparative purposes and to aid the interpretation of the n.m.r, spectra, Raman spectroscopy and differential pulse polarography were also applied. Of the eight n.m.r. resonances observed, two had already been reported: they stem from [PMo12O40]3– and [P2Mo18O62]6– Lines corresponding to [P2Mo5O23]6–, [PMo9O31(OH)3]6–, and [PMo11O39]7– were also identified. A controversy concerning the relative importance of the last two species has been resolved. Three lines could not be unequivocally assigned: one may correspond to [PMo10O34]3–, one to [PMo6O25]9–, while for the third there are no further data on which to base a suggestion. It is shown that various reports concerning molybdophosphate solutions are inconsistent with the pertinent 31P n.m.r. spectroscopic data.